EEPOET ON THE TETEACTINELLIDA. 
85 
The lamellae are slightly curved ; the concave may be spoken of as the inner face, the 
convex as the outer. Beneath the skin of the inner face is a network of subdermal 
canal-like cavities, running in a crooked course, chiefly longitudinally, i.e., radially from 
the base, and branching and anastomosing laterally. A similar but more widely marked 
network of subdermal canals occurs over parts of the outer surface. The skin of the 
inner surface is perforated by oval apertures from 0’08 mm. in diameter to 0‘254 by 
0'334 mm., one or sometimes two lying in an area of membrane bounded by the arms of 
adjacent trisenes and tangentially disposed oxeas. The pore-bearing area is depressed 
wdthin the spicular framework, and this produces the regular pitting already mentioned 
as characteristic of the inner surface. That of the outer surface is perforated by more 
numerous and smaller apertures about 0'05 by 0‘08 mm. in diameter, several lying 
together in the areas bounded by adjacent spicules. On removing the skin from the 
inner face, the open ends of transverse canals of small but somewhat uniform diameter 
are exposed ; on removing the skin from the outer face, the open ends of canals are 
similarly displayed, but these are of less uniform size, many being much larger than 
those of the inner faces. 
The oxeate spicules and triaenes are much subject to a rounding-off of the ends ; 
in one instance the usually slender, sharp-pointed microxea was found to have undergone 
the same modification ; the ends, which are roughened, are rounded off, at some distance 
from what would have been their normal position, and in addition the spicule has become 
swollen in the middle (centrotylote), so that it presents a very close resemblance to 
the centrotylote oxea, which occurs as the sole microsclere of some other sponges. 
The spirasters are present in a dense layer below the outer epithelium, and do not 
appear to be present elsewhere, metasters replacing them in the interior. The microxeas 
are far less numerous than in Podcillastra tenuilaminaris. 
In minute structure and the arrangement of the spicules the sponge resembles 
Pcecillastra schiilzii ; the flagellated chambers measure about 0‘0276 to 0'0316 mm. in 
diameter. 
Pcecillastra tenuilaminaris, Sollas (PI. V. figs. 17, 18). 
Normania tenuilaminaris, Sollas, Prelim. Account, Sci. Proc. Eoy. Dubl. Soc., vol. v. p. 186, 1886. 
Sponge (PI. V. figs. 17, 18). — A very thin lamellar wall 3 to 3 ‘5 mm. thick, irregu- 
larly curved, with an irregularly sinuous rounded margin ; surface generally but sparingly 
hispidated by projecting oxeate spicules ; no special hisjDidating fringe at the margin ; 
oscules minute, distributed evenly over one face of the sponge ; pores similarly dispersed 
over the opposite face. 
Spicules. — I. Megascleres. 1. Oxea, stout, fusiform, straight or curved, not sharply 
pointed, frequently rounded at one or both ends, and so reduced either to styles or a short 
cylindrical strongyle ; 3‘4 by 0‘042 mm. 
